Introducing the Notebook

To run the IPython console, type ipython in an OS terminal. There, you can write Python commands and see the results instantly. Here is a screenshot:

IPython console

The IPython console is most convenient when you have a command-line-based workflow and you want to execute some quick Python commands.

You can exit the IPython console by typing exit.

To run the Jupyter Notebook, open an OS terminal, go to ~/minibook/ (or into the directory where you've downloaded the book's notebooks), and type jupyter notebook. This will start the Jupyter server and open a new window in your browser (if that's not the case, go to the following URL: http://localhost:8888). Here is a screenshot of Jupyter's entry point, the Notebook dashboard:

The Notebook dashboard

The Notebook is most convenient when you start a complex analysis project that will involve a substantial amount of interactive experimentation with your code. Other common use-cases include keeping track of your interactive session (like a lab notebook), or writing technical documents that involve code, equations, and figures.

In the rest of this section, we will focus on the Notebook interface.

The dashboard contains several tabs:

A notebook is an interactive document containing code, text, and other elements. A notebook is saved in a file with the .ipynb extension. This file is a plain text file storing a JSON data structure.

A kernel is a process running an interactive session. When using IPython, this kernel is a Python process. There are kernels in many languages other than Python.

In Jupyter, notebooks and kernels are strongly separated. A notebook is a file, whereas a kernel is a process. The kernel receives snippets of code from the Notebook interface, executes them, and sends the outputs and possible errors back to the Notebook interface. Thus, in general, the kernel has no notion of a Notebook. A notebook is persistent (it's a file), whereas a kernel may be closed at the end of an interactive session and it is therefore not persistent. When a notebook is re-opened, it needs to be re-executed.

In general, no more than one Notebook interface can be connected to a given kernel. However, several IPython consoles can be connected to a given kernel.

To create a new notebook, click on the New button, and select Notebook (Python 3). A new browser tab opens and shows the Notebook interface as follows:

A new notebook

Here are the main components of the interface, from top to bottom:

There are two main types of cells: Markdown cells and code cells, and they are described as follows:

You can change the type of a cell by first clicking on a cell to select it, and then choosing the cell's type in the toolbar's dropdown menu showing Markdown or Code.

Markdown cells

Here is a screenshot of a Markdown cell:

A Markdown cell

The top panel shows the cell in edit mode, while the bottom one shows it in render mode. The edit mode lets you edit the text, while the render mode lets you display the rendered cell. We will explain the differences between these modes in greater detail in the following section.

Code cells

Here is a screenshot of a complex code cell:

Structure of a code cell

This code cell contains several parts, as follows:

• The Prompt number shows the cell's number. This number increases every time you run the cell. Since you can run cells of a notebook out of order, nothing guarantees that code numbers are linearly increasing in a given notebook.
• The Input area contains a multiline text editor that lets you write one or several lines of code with syntax highlighting.
• The Widget area may contain graphical controls; here, it displays a slider.
• The Output area can contain multiple outputs, here:
  • Standard output (text in black)
  • Error output (text with a red background)
  • Rich output (an HTML table and an image here)

The Notebook implements a modal interface similar to some text editors such as vim. Mastering this interface may represent a small learning curve for some users.

Keyboard shortcuts are available in the Notebook interface. Type h to show them. We review here the most common ones (for Windows and Linux; shortcuts for OS X may be slightly different).

Here are a few references: